Honing is used to correct hole geometry and also to prepare surfaces that require a specific finish or scratch pattern. Typical of the latter are piston bores or liners in internal combustion engines. On such oil lubricated moving part surfaces, it is customary to provide what is known as a plateau finish. A plateau finish is similar to a conventional finish, except that the peaks have been removed or flattened out. The finish attempts to duplicate the finish after the engine has been broken in, and removes or smooths out metal that would otherwise be removed by piston rings. A proper plateau finish contributes to the mechanical and environmental efficiency of the engine. This is usually accomplished by a two stage honing process including rough and finish honing.
Conventional honing tools are usually conventional stones or plated super abrasive tools. Most stones use vitrified, metal or resins bonds, and are similar to hard grinding wheels. Plated honing tools normally make use of super abrasives and consist usually of a single layer of abrasive attached to a metal surface by electrolytic plating. Inspection of the surfaces after use of these tools sometimes finds abrasive grains embedded in the metal surface, even though the honing operation is done under constant flushing with a lubricant or coolant. Abrasive contact with piston rings or other moving parts leads to premature wear, blow-by, or mechanical inefficiency, as well as environmental problems.
More recently, there has been developed a unique honing tool useful as a secondary or tertiary step honing tool which produces a superior honing finish in high production situations. An example of this type of tool is shown in Scheider et al., U.S. Pat. No. 5,216,847, issued June 8, 1993. A process for using the tool shown in such patent is disclosed in U.S. Pat. No. 5,331,775.
There is also disclosed in the copending application of Tyler et al., Ser. No. 08/052,366 filed Apr. 23, 1993, entitled "Honing Tool And Method Of Making", now U.S. Pat. No. 5,527,313 a somewhat similar disposable honing tool for honing operations less exacting than high production operations, such as engine rebuilding.
The tools described in the above patents or copending application comprise a bundle of tightly packed parallel monofilaments of relatively short extent, which bundle is secured in a holder. The holder is in turn mounted in the honing machine head and driven for rotation, usually on the axis of the bore, and for axial reciprocation within the bore. The tightly packed tips of the monofilaments of the projecting bundle form the working face of the tool. The material of the monofilaments is nylon or other suitable fairly rigid and tough plastic, having the abrasive mineral or grain homogeneously entrained therein throughout. The monofilament may have as much as about 30 to about 45% by weight of abrasive material. The compacted tips provide a working face which has sufficient flexibility or softness to avoid planting abrasive in the work surface, and yet which is aggressive enough to form the proper surface and plateau finish. The laterally compacted finger-like elements compliment each other to obtain stiffness and yet provide a degree of compliance to the tool. The compliance allows the tool to travel the surface and condition it even though it may have indentations and waviness.
While the abrasive monofilaments are tightly packed and such filaments are mutually self supporting, those filaments around the exterior of the bundle can flex to a limited extent away from the tip working face of the bundle. This peripheral flexing of the monofilaments of the compacted bundle is not normally a problem unless high tool pressures are used or the filaments have a high abrasive loading or content. The tough plastic material provides the tensile and modular strength to the extruded monofilaments and at high abrasive loading such as above 30-45%, such loading tends to weaken the monofilament. Such high abrasive loading with the peripheral flexing may cause premature failure and excessive wear of the filament. This problem in effect limits the amount of abrasive in the filaments.
While the yielding compacted tip surface is important to the proper functioning of the tool, particularly in secondary or tertiary operations, the amount of abrasive delivered to the work surface is a measure of the aggressiveness of the tool and its efficiency (work vs. time). It would, accordingly, be desirable to have a tool having all of the advantages of the yielding compacted tip surface, and yet with the ability to deliver more abrasive to the work surface per unit of time, and at a higher tool pressure.
In such U.S. Pat. No. 5,527,313 there is disclosed a low cost crimp method of making honing tools where a relatively narrow bundle of monofilaments is inserted in a rectangular metal holder with a thin deformable lip or rim which is swaged to grip the bundle in the forming process. No adhesive or other form of attachment to the holder is employed. While the process and tool provides a low cost disposable alternative to the larger and more costly precision made tools such as shown in U.S. Pat. No. 5,556,378 the size of the bundle is limited, and if one filament breaks or becomes loose, other filaments may become loose limiting the useful life of the tool. When the bundle is clinched in the process, the filaments tend to flare to some extent, both above and below the rim. The clinching forms a natural dovetail matching that of the bundle assisting in holding the bundle in place. Such tools also suffer from the same abrasive loading problems identified above. It would, accordingly, be useful if a solution to the abrasive loading problem would also enable the lower cost crimp tools to be made in larger sizes without fear of excessive filament breakage or filaments becoming loose or dislodged, while at the same time delivering more abrasive to the work surface per unit of time at a higher application. It would also be useful to be able to make the larger more precise compacted tip filament tools with less precision in formation and attachment of the bundle to the holder while nonetheless improving the performance of the tool.